IT can't be particularly pleasant being Steven Green, until recently a private first class in the US Army.

Not only is he a seriously disturbed young man with a severe personality disorder (the army's description, not mine), but this week he goes on trial in Kentucky for raping a 14-year-old Iraqi girl and then slaughtering her and her family. At the same time, five other soldiers from the 502nd Infantry Regiment will face court martial for their complicity in the crime.

There are lots of arcane military legalities to explain why Green is being tried before a civilian court while his mates will face court martial - he had been discharged from the army and was a civilian at the time of his arrest - but the cases are less about legal niceties and more about how a man like Green came to be in Iraq in the first place. He was brought up in Midland, Texas, ironically also President Bush's hometown, and from the start he was trouble. Drink and drugs fuelled an already violent personality and he was heading down the road to perdition.

Like many others who found themselves on the same track, he joined the army. On one level you could say that it was a smart move. In place of his aimless existence in small-town Texas he discovered companionship, a sense of belonging, pride in wearing a uniform and the respect that goes with it. It seems that he thrived during basic training and emerged at the other end if not the finished article, then at least someone who had shown himself amenable to the military life.

Except that something was missing.

Basic training had made Green look like a soldier but his mental outlook was still the mess that it had been back in Midland. In the past, the US Army placed a high premium on getting it right during basic training, believing with good reason that this period was a vital staging post for young people making the transition from civilian to warrior.

Whenever American drill-sergeants were accused of being overly tough on their young charges, they would reply:

"Give me control of their instinct and you can have their reason."

That didn't happen in Green's case and when he was shipped out to Iraq in the summer of 2005 he was that dangerous beast: a man with no selfdiscipline in charge of a gun. The experience of war unnerved him. He found that it was not a computer game but a hellish business in which people literally get blown to pieces and died not like heroes but screaming in agony. One night, he had had enough and the demons in his head took him out of camp and into the house of a blameless Iraqi family in Al Mahmudiyah, slap bang in the heart of the Sunni Triangle.

It's now clear that Green had slipped through the net during basic training and that his instructors failed to pick up on the fact that he was grotesquely unsuited to being a soldier. But here's the rub: such is the demand for recruits at a time when the US armed forces are over-stretched that the system has been subtly re-focused. Instead of insisting on checks to weed out the misfits, the emphasis has been changed to make sure that as many recruits as possible get through basic training. At a time when Iraq hovers on the brink of civil war, the deaths in Al Mahmudiyah may be just another set of statistics but that they exist at all begs the age-old question. When lives are at stake, who guards the guardians?